POSTIRRIGATION BREEDING PATTERNS OF SURFACE-WATER MOSQUITOS IN THE MAHAWELI PROJECT, SRI-LANKA, AND COMPARISONS WITH PRECEDING DEVELOPMENTAL PHASES

A 2-yr (1988-1989) survey of mosquitoes breeding in surface water was done in an area of the Mahaweli Project of Sri Lanka that underwent ir rigation development and human settlement during the preceding 3 yr. I n total, 78,649 immatures of 42 species were collected during the surv ey. Species of medical importance in the area were Anopheles annularis van der Wulp, An. culicifacies Giles, An. jamesii Theobald, An. niger rimus Giles, An. subpictus Grassi, An. vagus Doenitz, An. varuna Iyeng ar, Mansonia annulifera (Theobald), Ma. uniformis (Theobald), Culex fu scocephala Theobald, Cx. gelidus Theobald, Cx. pseudovishnui Colless, Cx. tritaeniorynchus Giles, and Cx. vishnui Theobald. These and other species used breeding habitats associated with irrigation development (i.e., canals, reservoirs, seepage pools, and rice fields) as well as natural habitats (i.e., rainwater pools, riverbed pools, streams, and marshes). Trends in the use of breeding habitats that were observed wi th the onset of irrigated rice cultivation in 1987, continued during t he period under stable irrigation in 1988 and 1989. Mosquito species r ichness declined, but species equitability (as indexed by Shannon-Weav er diversity values) did not change. The overall study showed that eco system changes concomitant with irrigation development in the Mahaweli Project resulted in long-term changes in the composition of the mosqu ito fauna, which was characterized by the increasing dominance of spec ies with the potential to transmit human pathogens.